1. Field of the Invention
The present invention relates to an optical disc discriminating device and discriminating method suitable for a single surface reading type optical disc.
2. Description of the Related Art
A compact disc (CD) is formed, as is well known, by recording digital audio signal in the form of physical pits to the single surface of a transparent disc having diameter of 12 (or 8) cm and thickness of 1.2 mm and then evaporating a reflection layer on the recording surface in view of reading the recording surface via a disc with an optical pickup provided opposite to the other surface of disc.
In the CD of the related art, the 16-bit PCM with the sampling frequency of 44.1 kHz has been employed for digital recording.
Therefore, such a CD has a problem that a frequency response of the audio signal has been limited to 20 kHz and it has been difficult to perfectly overcome analog audio sound and flexibility in the manufacturing side and high end audio area.
Considering such background, the applicants of the present invention have proposed a "Super-Audio CD" which has expanded the frequency response of audio signal up to 100 kHz to realize further higher sound quality and assures compatibility to an ordinary CD by introducing, for example, the one bit direct stream digital (DSD) technique with the sampling frequency of 2.8224 MHz.
This super audio CD is formed, as illustrated in FIG. 5, as a "hybrid disc" in which the substrate of an ordinary CD is divided into two sections in the thickness direction and a high density layer is added to the intermediate part of these two sections.
Namely, as illustrated in FIG. 5, on the upper surface 1 consisting, for example, of polycarbonate resin of the hybrid disc Dhy, a total reflection type CD compatible layer 2 is formed and it is protected by a protection layer 3.
Moreover, to on the lower substrate 4 consisting, for example, of polycarbonate resin, a semi-transmitting high density (HD) layer 5 is formed and it is then adhered with the upper substrate 1 via the protection film 6. As the hybrid disc Dhy, a disc has the thickness of 1.2 mm like the compact disc CD.
The CD compatible layer 2 and high density layer 5 are provided opposed with each other keeping distance of about 0.6 apart mm and these layers are read respectively from the same side (lower side in the figure) with a CD pickup 7 and HD pickup 8.
Specifications of the CD compatible layer 2, high density layer 5, CD pickup 7 and HD pickup 8 explained above are indicated in FIG. 6. As will be understood from FIG. 6, the CD pickup 7 uses an infrared laser beam, while the HD pickup 8 uses red laser beam in the shorter wavelength.
Meanwhile, in these years, a DVD (Digital Versatile Disc) which has outstandingly enhanced the recording density even in the same disc size as CD to realize the recording of compressed moving video information exceeding two hours, for example, with the large capacity of 4.7 GB in a single surface and single layer and its reproducing device have been proposed.
A disc Ds of single surface and single layer type among DVD is formed, as illustrated in FIG. 7A, by recording the compressed moving video information in the form of physical pits to the single surface of the transparent substrate 11 in the thickness of 0.6 mm, evaporating a reflection layer 12 to the recording surface and then adhering the one substrate to the disc 14 of the same thickness via the protection film 13. The recording surface is read via the substrate 11 with an optical pickup 15 provided opposite to the other surface of substrate 11.
A disc Dd of the single surface, double layer type among DVDs is formed, as illustrated in FIG. 7B, by forming physical pits to the single surface of transparent substrate in the thickness of 0.6 mm, evaporating a reflection layer 12 and then protecting the surface with a protection film 13. Moreover, the physical pits are also formed on one surface of the substrate 1 in the same thickness, a semi-transparent layer 17 is evaporated and it is then protected by a protection film 18. These substrates are adhered in such a manner that both protection layers 13, 18 are provided in contact.
The semi-transparent layer 17 and reflection layer 12 are provided opposed with each other keeping a distance of about several tens of .mu.m and these layers are read respectively from the same side (lower side in the figure) through the substrate 16 with optical pickups 15a, 15b provided opposed opposite to the other surface of the substrate 16.
In the case of single surface and single layer DVD, specifications of the reflection layer 12 and optical pickup 15 are almost the same as those of high density layer 5 and HD pickup 8 as indicated in FIG. 6.
In the case of single surface and double layer DVD, line density is specified to the value reduced by about 10% and its capacity is 8.5 GB in order to compensate for reduction in an amount of reproduced light beam.
A player for reproducing a DVD explained above has an essential condition to reproduce the ordinary CD and an optical pickup having the function assuring compatibility for DVD/CD loaded for the purpose of cost reduction is provided with various devices such as double focusing system using a hologram, objective lens changeover system, aperture limiting system and double laser system.
In the case of reproducing a super audio CD as explained above with a CD player of the related art, the infrared laser beam emitted from the optical pickup loaded to this player is transmitted through a high density layer 5 and is then reflected by the CD compatible layer 2. That is, the recorded data of the CD compatible layer 2 can be read in the same manner as the reproduction of the ordinary CD.
Moreover, in the case of reproducing a super audio CD with a player corresponding to the super audio CD, the red laser beam emitted from the optical pickup loaded to this player is reflected by a high density layer 5 to read the recorded data of the high density layer 5 and thereby the reproduced sound which is remarkably improved in the sound quality than that of the ordinary CD can be obtained.
Here, the player corresponding to a super audio CD is required to be able to reproduce the ordinary CD as in the case of or rather than the DVD player explained above.
Therefore, the player corresponding to the super audio CD is required to discriminate, before the reproducing operation, whether an optical disc loaded is the ordinary CD or super audio CD and automatically select the optimum reproducing circuit and software in view of reproducing the loaded optical disc in the optimum reproducing condition.
Particularly, in the case of loading an optical pickup having the DVD/CD compatible function explained above to reduce the cost of the player corresponding to the super audio CD, it is required to discriminate the loaded optical disc.